Handwriting expert witnesses typically do not state with certainty that a particular handwriting sample came from a particular individual, even if the goal of litigation is to prove that one person wrote a particular document. Instead, handwriting experts will express their opinion as to whether the characteristics of the handwriting on the document in question are consistent or inconsistent with the known sample used for comparison. Expert Institute.
Handwriting analysis is a useful tool that can be used in conjunction with other evidence to argue a case, but should not ultimately decide the fate of a defendant or be used to definitively declare whether a handwritten communication originated from a particular subject. However, this concept has been disregarded in parts of the Zodiac community, who insist they can look at an nth generation copy of a letter and determine it's an obvious fake simply by staring at it. There are also individuals who will claim that there is a universal arbiter pertaining to which communications are genuine or otherwise, despite disagreement between questioned document examiners and handwriting analysts connected to the Zodiac scene itself.
In fact, many "so-called experts" have been discredited in recent years by a lack of due diligence, aligning themselves behind amateur researchers who are promoting a suspect, in conjunction with the release of a new Zodiac book. There is the infamous case of the JonBenet Ramsey murder, in which a three-page ransom note was supposedly left behind in the residence of the parents. Many document examiners have come to the conclusion it was written by the mother of JonBenet Ramsey, while others have dismissed this entirely. The point being, when you have disagreement in accredited experts within the field, what is the point of an authenticated list of Zodiac communications by a universal arbiter of truth or otherwise. Individuals who just look at these communications through a magnified lens, yet don't examine these communications in depth regarding the wider context of the Zodiac case - a case that has been examined far more thoroughly over 50 years since many of these determinations were made. What is far more important, is examining the content of a communication and how it fits into the overall story. One such example is the widely discredited Fairfield letter mailed on December 16th 1969, which has been routinely dismissed as being written by an amateurish and infantile hoaxer. Despite reasoning offered for its authenticity that is widely ignored, the recent solving of the 340 cipher by David Oranchak, Sam Blake and Jarl Van Eycke has provided further evidence to its authenticity through the identification of words in the Z340 and Z38 cryptograms, specifically identified by the author of the sister communication on December 7th 1969, who is undeniably the author of the December 16th 1969 letter. This too has been routinely ignored, because sometimes you have to accept that no amount of evidence will move a fixed mind - even when the preponderance of evidence points strongly in one direction. For some, no amount of evidence will ever make a difference. Just ask somebody who believes the Fairfield letter was created by a hoaxer, what are the strongest five arguments given by people in favor of it being genuine, and they will almost certainly fail to give you one or two (if any). The reason why - because they have already made up their mind without having read any counter arguments to their case - which is solely based on looking at the letter and nothing more. Enter the discussion and use cogent reasoning to argue against the points suggested for the authenticity of the Fairfield letter, as opposed to just saying "It's an obvious fake", bereft of any foundation for concluding such a resounding conclusion.